EP0508897B1 - Verfahren und Vorrichtung zur automatischen Scharfeinstellung einer CCD-Kamera mittels einer DCT - Google Patents

Verfahren und Vorrichtung zur automatischen Scharfeinstellung einer CCD-Kamera mittels einer DCT Download PDF

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Publication number
EP0508897B1
EP0508897B1 EP92400998A EP92400998A EP0508897B1 EP 0508897 B1 EP0508897 B1 EP 0508897B1 EP 92400998 A EP92400998 A EP 92400998A EP 92400998 A EP92400998 A EP 92400998A EP 0508897 B1 EP0508897 B1 EP 0508897B1
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Prior art keywords
image
coefficients
digital
calculating
control signal
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EP92400998A
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English (en)
French (fr)
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EP0508897A1 (de
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Jamal Baina
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Telediffusion de France ets Public de Diffusion
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Telediffusion de France ets Public de Diffusion
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/60—Control of cameras or camera modules
    • H04N23/67—Focus control based on electronic image sensor signals
    • H04N23/673—Focus control based on electronic image sensor signals based on contrast or high frequency components of image signals, e.g. hill climbing method

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  • the invention relates to a method for the automatic focusing (autofocusing) of an image forming device, the image forming device comprising a variable focal length optics controlled by a control signal to form an image of an observed scene and means for providing a digital signal representative of the image formed which has a definition depending on the focal length of the optics.
  • An object of the invention is to propose a method for the automatic development of an image forming device, intended to be used in a computer vision system, which takes advantage of the functionalities of the equipment constituting the computer vision system.
  • the calculations are carried out in the pixel space, according to the invention on the contrary, they are carried out in the frequency space.
  • the basic idea of the invention is that the frequency coefficients of a cosine transform are lower when the image is defocused. According to a preferred mode, a characteristic value of the focusing is directly reached by summing the coefficients of the discrete cosine transform (TCD) for at least one area of the image, hence few calculations.
  • TCD discrete cosine transform
  • the invention extends to a vision system comprising a video camera having a variable focal length optics controlled by a control signal to provide a video signal representative of an image having a definition dependent on the focal length of the optics, a means for digitizing the video signal connected to the video camera to supply digital image data, means for processing digital image data connected to the digitizing means, and means for controlling the control signal for varying the focal length of the optic, characterized in that the means for controlling the control signal comprises a calculation means connected to the digitization means for transforming the digital image data into coefficients of transform in discrete cosine and a calculation means and control connected to the first calculation means for slaving the control signal in response to the values of said coefficients so as to automatically obtain the d maximum finishing the image.
  • the computer vision system comprises an image forming device 10, for example a video camera, which supplies a video signal SV representative of a formed image, a digitizing circuit such as 20 connected to the output of the video camera to digitize the video signal and provide digital image data DN (pixels), a processing unit 25, such as a computer, connected to the digitizing circuit to perform processing operations on digital image data and a servo circuit such as 30 for automatically focusing the video camera.
  • image forming device 10 for example a video camera, which supplies a video signal SV representative of a formed image
  • a digitizing circuit such as 20 connected to the output of the video camera to digitize the video signal and provide digital image data DN (pixels)
  • a processing unit 25 such as a computer, connected to the digitizing circuit to perform processing operations on digital image data
  • a servo circuit such as 30 for automatically focusing the video camera.
  • the processing operations are linked to a particular application: remote monitoring, industrial robotics or other.
  • the image forming device can just as easily be a semiconductor sensor providing digital image data DN directly without going outside the scope of the invention.
  • the image forming device comprises a variable focal length optic such as 15 provided with a motor 16 for moving the elements of the optics in response to an electrical control signal supplied by the servo circuit 30 in order to obtain automatically a sharp image.
  • This electrical control signal is represented by the symbols + F, -F which are for example electrical voltages applied selectively to the terminals of the motor 16, the application of these voltages, respectively, resulting in displacement, in one direction or in the other according to the applied voltage of the focal point of the optics with respect to the plane of the screen of the imaging device.
  • a parameter AS of global activity of the image is then calculated from the parameters ace of local activity of the image previously calculated for all the blocks 120 formed according to the following relation: where x, y are here the indices of the parameters as assigned to the blocks of coefficients, L, M are the dimensions in number of blocks of digital image data of the area of the image on which it is desired to focus, that is to say to focus;
  • control signal is controlled to obtain the maximum value of the parameter AS of overall activity of the image, that is to say that the calculation and processing unit 35 generates signals SF and TF after each taking an image and processing the TCD coefficients as described above so as to converge the AS parameter, during successive image captures for different focal lengths, up to a maximum value.
  • the process of obtaining the maximum value of the parameter AS is preferably implemented by program.
  • the calculation and control unit 35 is shown interposed between the digitization circuit 20 and the calculation processor of TCD 40.
  • the calculation and control unit 35 which can be the computer constituting the processing unit 25 receives as input the values L, M which define an area of the image to be focused. These values L, M can be supplied automatically by the processing unit 25 or by an operator via a data entry keyboard (not shown).
  • the calculation and control unit 35 determines the blocks 110 of digital data to be supplied to the calculation processor of TCD 40 to be transformed into blocks 120 of coefficients TCD.
  • the focusing is done automatically on the complete image formed by the camera or on a part of it.
  • the method for the automatic focusing of a controllable variable focal length camera uses only electronic means, calculation processors, which are in common use in image coding systems and are inexpensive.
  • it will be possible to design, in particular for remote monitoring applications, algorithms for automatic scanning of images allowing the optics of the camera to be developed successively on different areas of the images.
  • the interactive selection of the image area to focus is of interest in videoconferencing applications.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Automatic Focus Adjustment (AREA)
  • Focusing (AREA)
  • Studio Devices (AREA)

Claims (6)

  1. Verfahren zur automatischen Scharfeinstellung in einer Vorrichtung zum Erstellen von Bildern (10), wobei diese Vorrichtung eine Optik (15) mit variabler Brennweite umfaßt, die über ein Befehlssignal gesteuert wird, um eine Abbildung einer beobachteten Szene zu erstellen, sowie Mittel (20) zum Bereitstellen von repräsentativen digitalen Daten (DN) eines erstellten Bildes, dessen Auflösung von der Brennweite der Optik abhängt. Dieses Verfahren, bei dem das Befehlssignal der Abbildungsvorrichtungsoptik, ausgehend von einem für das Bild repräsentativen digitalen Signal, so gesteuert wird, das man die höchste Bildauflösung erhält, ist
    dadurch gekennzeichnet, daß das digitale Signal durch Transformation der digitalen Bilddaten erzeugt wird, welche durch eine diskrete Kosinustransformierte (TCD) in Koeffizienten umgewandelt wird, die für die Raumfrequenzen des Bildes repräsentativ sind.
  2. Verfahren gemäß Anspruch 1,
    dadurch gekennzeichnet, daß es eine Zählung der positiv genommenen Koeffizienten anwendet.
  3. Verfahren gemäß Anspruch 1 oder 2,
    dadurch gekennzeichnet, daß es die folgenden Schritte umfaßt:
    - die digitalen Bilddaten werden zusammengefügt, um digitale Datenblöcke (110) zu bilden, die repräsentativ für einen Bildbereich sind;
    - jeder Datenblock wird in einen Block (120) von diskreten Kosinustransformiertenkoeffizienten transformiert;
    - für Jeden Koeffizientenblock wird ein Parameter as der örtlichen Bildaktivität gemäß der folgenden Beziehung berechnet:
    Figure imgb0009
     wobei Fu,v ein Koeffizient aus dem Koeffizientenblock ist,
    u,v die Indizes des Koeffizienten im Koeffizientenblock sind,
    N eine Dimension des Koeffizientenblocks ist;
    - ausgehend von den örtlichen Bildaktivitätsparametern as, wird ein globaler Bildaktivitätparameter AS gemäß der folgenden Beziehung berechnet:
    Figure imgb0010
     wobei x,y die Indizes der Parameter as sind, die den Koeffizientenblöcken zugeordnet sind,
    L,M die Zahlendimensionen der digitalen Bilddatenblöcke des Bildbereichs sind;
    - das Befehlssignal wird so gesteuert, das man den maximalen Wert für den Parameter AS der gesamten Bildaktivität erhält.
  4. Videosystem, welches eine Videokamera (10) umfaßt, die eine Optik (15) mit variabler Brennweite hat, welche durch ein Befehlssignal gesteuert wird, um ein repräsentatives Videosignal eines Bildes, dessen Auflösung von der Brennweite der Optik abhängt, zu liefern; ferner eine Digitalisierungsvorrichtung (20) für das Videosignal, das mit der Videokamera verbunden ist, um digitale Bilddaten zu liefern; eine Verarbeitungsvorrichtung (25) für die digitalen Bilddaten, die mit der Digitalisierungsvorrichtung verbunden ist, sowie Steuerungsmittel (30) des Befehlssignals, um die Brennweite der Optik zu ändern,
    dadurch gekennzeichnet, daß das Steuerungsmittel des Befehlssignals Mittel zur Berechnung (40) umfaßt, die mit der Digitalisierungsvorrichtung verbunden sind, um die digitalen Bilddaten in diskrete Kosinustransformiertenkoeffizienten umzuwandeln sowie eine Berechnungs- und Steuerungsvorrichtung (35, 36), die mit den ersten Mitteln zur Berechnung verbunden ist, um das Befehlssignal in Beantwortung der Koeffizienten zu steuern, damit die höchste Bildauflösung automatisch erzielt wird.
  5. Anspruch gemäß Anspruch 4, wobei die Berechnungs- und Steuerungsvorrichtung zwischen der Digitalisierungsvorrichtung und den Mitteln zur Berechnung eingebracht wird und die für einen Bildbereich repräsentativen digitalen Bilddaten als Antwort auf eine Information des Bildbereichs an die Berechnungsmittel überträgt, wobei die Mittel zur Berechnung und zum Steuern so ausgebildet sind, das sie das Befehlssignal steuern, bis der Bildbereich die maximale Auflösung aufweist.
  6. System gemäß Anspruch 4 oder 5,
    dadurch gekennzeichnet, daß die Mittel zur Berechnung und zur Steuerung so ausgebildet sind, daß sie die Koeffizienten addieren, die alle positiv genommen werden.
EP92400998A 1991-04-11 1992-04-09 Verfahren und Vorrichtung zur automatischen Scharfeinstellung einer CCD-Kamera mittels einer DCT Expired - Lifetime EP0508897B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9104420A FR2675330B1 (fr) 1991-04-11 1991-04-11 Une methode et un systeme pour la mise au point automatique d'une camera utilisant la tcd.
FR9104420 1991-04-11

Publications (2)

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EP0508897A1 EP0508897A1 (de) 1992-10-14
EP0508897B1 true EP0508897B1 (de) 1995-12-27

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DE (1) DE69207043T2 (de)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012022713A1 (de) 2010-08-18 2012-02-23 Robert Bosch Gmbh Vorrichtung zur unterstützung einer fokussierung einer kamera

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2711030B1 (fr) * 1993-10-08 1995-12-08 Telediffusion Fse Système de traitement d'images numérisées et son application à la compression-décompression de ces images ou à un dispositif d'autofocalisation pour caméra vidéo.
FR2711812B1 (fr) * 1993-10-27 1996-01-05 Telediffusion Fse Procédé et système de commande automatique du diaphragme du dispositif de formation d'image.
FR2711813B1 (fr) * 1993-10-27 1996-01-12 Telediffusion Fse Procédé et dispositif de focalisation automatique d'un objectif.
DE102013224704A1 (de) 2013-12-03 2015-06-03 Robert Bosch Gmbh Verfahren zur automatischen Fokussierung einer Kamera
CN113114934B (zh) * 2021-03-31 2022-08-05 太原理工大学 尿红细胞多焦距视频采集方法与系统

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US4752831A (en) * 1986-05-20 1988-06-21 Polaroid Corporation Focusing system for camera apparatus
US4814889A (en) * 1987-10-07 1989-03-21 General Electric Company Automatic focussing system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012022713A1 (de) 2010-08-18 2012-02-23 Robert Bosch Gmbh Vorrichtung zur unterstützung einer fokussierung einer kamera
DE102010039431A1 (de) 2010-08-18 2012-02-23 Robert Bosch Gmbh Vorrichtung zur Unterstützung einer Fokussierung einer Kamera

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FR2675330A1 (fr) 1992-10-16
FR2675330B1 (fr) 1995-12-15
EP0508897A1 (de) 1992-10-14
DE69207043D1 (de) 1996-02-08
DE69207043T2 (de) 1996-09-19

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